We almost always brew 10 gallon batches. We're ready to go today but I stupidly only purchased yeast for a 5 gallon batch (1 vial) and all the beer stores are closed today. The way I figure it, there are 2 possible options: 1) cut the recipe in half and only brew 5 gallons; or, 2) brew the 10 gallons and wait until tomorrow to pitch the yeast in the second fermenter. Can we brew the wort today and pitch it tomorrow? Can you sit on a batch for 24 hours? What is the maximum amount of time you can wait to pitch the yeast?

Some people do cool overnight, so they pitch as much as 24 hours later. Your success, and how long you can get away with waiting, depends on how sterile your wort is. The longer you wait the more time contaminating bugs will have to grow before being out-competed by the yeast. The less bugs you start with the fewer bugs there are to grow.

I'd suggest taking some extract and getting a 2 quart starter going as early as possible. You might get a doubling in number by the time you go to bed tonight, so you could pitch then. Or pitch the starter first thing in the morning.